The invention relates to a method for the detection of surface defects of a component or of any other object and to a device for the carrying out of such a method.
Various methods are already known for the detection of surface errors of components. In so-called dark field lighting, the surface of the component is radiated with light from a light source from the side. The light radiated back by the surface of the component is detected by a sensor or a camera, by a CCD camera for example. The image detected by the sensor can be evaluated and/or stored. Dark field lighting is in particular used for the detection of scratches or similar surface defects. In this respect, the surface of the component is illuminated such that light only enters into the optical sensor from the site of the defect, that is, of the scratch.
To illustrate the known method of dark field lighting
FIG. 1 shows a device for the detection of surface defects of a component in a schematic side view; and
FIG. 2 shows a modified device in accordance with FIG. 1. The device in accordance with FIG. 1 includes two light sources 4, 4′ for the radiation of the surface of a component 5 from a respective side direction and a CCD camera 2 having a sensor for the detection of the light radiated back from the surface of the component 5. The light sources 4, 4′ are disposed opposite one another. They are arranged symmetrically to the center axis of the CCD camera 2. Directed light from the light sources 4, 4′ is incident onto the surface of the component 5.
The measured zone A is determined by the aperture 6 of the CCD camera 2 and the spacing of the CCD camera 2 from the component 5. The light sources 4, 4′ are arranged such that no light enters into the CCD camera 2 by the reflection on the surface of the component 5. The light source 4 radiates directed light from the left hand side onto the measured zone A at an opening angle α. The lower boundary ray 7 is incident to the surface of the component 5 at an angle β in the left hand end point 8 of the measured zone A and is reflected from there as a beam 9. The arrangement is made such that the reflected beam 9 is not incident into the CCD camera 2, but is radiated below the CCD camera 2.
The upper boundary ray 10 from the light source 4 leads to the right hand end 8′ of the measured zone A and is reflected from there at an angle γ which is smaller than the angle β which is likewise not incident into the CCD camera 2, but is radiated below the CCD camera 2.
The light source 4′ is disposed on the oppositely disposed side of the measured zone A. The light radiated from this light source 4′ onto the measured zone A is also not incident into the CCD camera 2 on the reflection on the surface of the component 5.
The methods and devices in accordance with FIG. 1 are known from various pre-publications, for example from DE 20 2005 011 807 U1, DE 10 2004 026 375 A1, DE 10 2004 058 778 A1 and DE 10 2005 031 490 A1.
In dark field lighting in accordance with FIG. 1, the light radiated from the light sources 4, 4′ is radiated past the optical sensor in the CCD camera 2 in the manner visible from FIG. 1 with a defect-free surface of the component 5. From the view of the CCD camera 2, the measured zone A appears dark with a defect-free surface of the component 5.
If there is a scratch or a similar defect on the surface of the component 5, the light radiated from the light sources 4 and/or 4′ is radiated back into the CC camera 2. Scratches on the surface of the component 5 can be recognized in this manner.
The sensitivity of the measurement is the larger, the smaller the angles β and γ are at which the rays 7, 10 or 7′, 10′ and the rays between them are incident onto the measured zone A. It is, however, frequently necessary for mechanical reasons that the light sources 4, 4′ have to observe a specific minimum spacing from the surface of the component 5. The angles β und γ and the angles disposed therebetween are hereby increased.
An example for this is shown in FIG. 2. The angles β and γ increase due to the increase in the spacing of the light sources 4, 4′ from the surface of the component 5. The reflected rays 9, 9′ of the lower boundary rays 7, 7′ enter into the CCD camera 2 and onto its sensor.
To prevent this and to be able to increase the sensitivity, the angles β and γ can be reduced in that the side spacing of the light sources 4, 4′ from the measured zone A is increased. However, the total arrangement or the device in which the light sources 4, 4′ are located is hereby also increased. Since a specific spacing of the light sources 4 from the surface of the component 5 has to be observed, either the sensitivity therefore decreases or the construction size of the device or of the inspection arrangement increases.